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Lady Bird Lake was upgraded to “suspect” status because mussels or their larvae have been found at least once after the Lower Colorado River Authority found several larvae in a plankton sample, according to a statement from the Texas Parks and Wildlife Department.

Lake Austin is considered infested once wildlife officials confirmed an established, reproducing population of zebra mussels. Texas Parks and LCRA staff found adult zebra mussels and larvae in multiple locations, including Tom Miller Dam and the Pennybacker Bridge, wildlife officials said.

Zebra mussels can not only harm native freshwater species, but they also can affect water clarity, cause algae blooms, litter beaches with sharp shells, clog water intakes on hydroelectric facilities, and damage boats and motors.

Monica McGarrity, whose team at Texas Parks and Wildlife monitors aquatic invasive species, said that once zebra mussels appeared in the Colorado River basin, they were likely to spread downstream.

“But downstream dispersal doesn’t spread zebra mussels to new river basins – boats do — and boats can spread them downstream more quickly,” she said.

McGarrity urged boat owners to “protect other river basins and prevent zebra mussels from spreading more quickly to other reservoirs by being extremely diligent about cleaning, draining and drying their boats and other gear every time they visit any lake or river.”

Austin city officials also are urging swimmers to thoroughly clean and dry all swimsuits, water shoes and other gear after swimming in Lake Austin or Lady Bird Lake before visiting any local swimming holes, including Barton Springs Pool.

According to the Texas Parks and Wildlife Department:

14 bodies of water in five river basins throughout the state, including Lake Austin, are infested with zebra mussels.

Five bodies are considered “positive,” meaning zebra mussels have been detected on more than one occasion

Three bodies, including Lady Bird Lake, are suspected of having zebra mussels.

Texas law prohibits anyone from intentionally possessing or transporting living or dead zebra mussels.

Boaters are required to drain all water from all craft, powered or unpowered, before leaving or entering rivers and lakes so zebra mussels and other invasive species don’t spread.

Wildlife officials say zebra mussels can survive for days in or on boats moved from a lake.

Zebra mussel DNA was identified in at least 10 other bodies of water in Texas during routine sampling in 2017, wildlife officials said.

Brian Van Zee, inland fisheries regional director for Texas Parks, said the presence of DNA is an alert for biologists and underscores the need for boaters to be vigilant about cleaning and draining their watercraft.

“Even though you may not see them, microscopic hitchhikers could still be hiding in your equipment,” he said.

CORRECTION: This article has been updated from a previous version that incorrectly described how zebra mussels affect water clarity. Zebra mussels have been known to consume enough plankton to increase water clarity.